The present invention relates to tamper-evident closures and methods of manufacture therefor.
Tamper-evident closures of various types have been used in the past on containers to enable the user of a product to determine whether the container has been opened. Such closures have commonly been made of aluminum or plastic. One type of closure includes an upper cap portion and a lower ring portion having a failure line, or line of weakness formed about its circumference. When the cap is removed, the closure breaks along the failure line, leaving a lower portion of the ring separate from the rest of the closure.
Closures of this type are described in copending U.S. patent application Ser. No. 467,873, which is assigned to the assignee of this application and is incorporated herein by reference, and in U.S. Pat. Nos. 4,322,009; 4,205,755; 3,929,246; 3,673,761 and 4,217,989.
One method of manufacturing closures of the above-described variety involves molding a plastic blank having a plurality of lugs connecting the cap portion to the lower portion of the ring, then forming a circumferential cut through the ring adjacent the lugs with a knife or the like, leaving the connecting lugs intact. One difficulty with this type of manufacture is that it is difficult to mass produce closures in this manner with acceptable tolerances. If the cut is too shallow, the lower portion of the ring may not separate properly from the upper portion of the ring upon removal of the closure. This can make the closure difficult to remove, or, in some types of closures, might cause the lower portion of the ring to remain attached to the upper portion after removal, which would defeat the tamper-indicating function of the closure. If the circumferential cut is too deep, it may penetrate the lugs and cause a failure of one or more of the lugs during installation of the closure on its associated container. Such a failure is undesirable not only because it may create a false indication that the closure has been tampered with, but also because the result may be aesthetically unattractive.